This invention relates to x-ray microscopes of the type wherein the object is illuminated coherently or at least partially coherently via a condenser with quasimonochromatic x-radiation, and is imaged enlarged by means of a high-resolution x-ray objective in the image plane. The term "microscope of the type described," as used in this application, means a microscope of this type described above.
Such x-ray microscopes are described, for instance, in Part IV of the book "X-Ray Microscopy" by G. Schmahl and D. Rudolph, published 1984 by Springer-Verlag. Pages 192 to 202 of this book described an x-ray microscope in which each focusing element, and therefore condenser and x-ray objective, is developed as a zone plate. Such a zone plate consists of a plurality of very thin rings, for instance of gold, which are applied on a thin support foil, for instance of polyimide. These rings for a circular grating with radially increasing line density.
The zone plates refract the impinging monochromatic or quasi-monochromatic x-radiation of the wavelength and thus effect an imaging. Quasi-monochromatic radiation means radiation of a certain bandwidth .DELTA..lambda., this bandwidth being established in connection with zone plates by the relationship .lambda./.DELTA..lambda..apprxeq.p.m, where p=number of lines, and m=number of the order of diffraction still to be covered.
In such known x-ray microscopes, the contrast in the image is obtained by photoelectric absorption in the object, that is, structures are imaged which effect an amplitude modulation of the x-rays passing through.
Particularly suitable is the wavelength range of x-ray radiation between 2.4 nm and 4.5 nm, i.e., between the oxygen K edge and the carbon K edge. This region is also known as the water window, since here water has approximately a ten times higher transmission than organic materials. With it, organic materials can be examined in this wavelength region and thus cells and cell organelles in a living state.
The resolution obtained up to now in x-ray microscopy is better by approximately a factor of ten than in optical microscopy, a further increase in the x-ray microscope resolution by about one order of magnitude being still possible. In this connection, the limiting resolution in the x-ray microscopy of amplitude structures is determined by the radiation load of the objects to be examined.